1. Field of the Invention
The present invention relates to antennas and more particularly to an apparatus and method for scanning a high frequency antenna across a predetermined field of view. The invention further relates to a scanning antenna utilizing a series of magnetically modulated current shunts to alter the phase center of a horn type antenna for tracking a moving signal source.
2. Background
There has been an ongoing need to develop antennas capable of scanning a field of view for receiving signals. In some applications the signals are received from different sources having differing positions within a predefined field of view. In other applications, signals are detected or received from a single moving source, or series of such sources, that traverse along a reasonably well defined path across the field of view. In this latter application it is desirable to track the antenna along with the target or source in order to allow or optimize reception.
Most targets of interest are moving at fairly high speed or occupy a small aperture size in the far field view of an antenna. Received signals are also very directional having a large off-axis attenuation or power drop off that is very steep beyond 10 or more degrees from center. These factors make physical motion of the antenna for real time tracking undesirable, especially for advanced communications. Physical placement and motion of the antenna for modern communications requires high precision and reproducibility, neither of which are obtainable with coarse mechanical systems. Mechanically moving an antenna with high precision is very expensive and generally too slow for modern applications.
Therefore, non-mechanical or so called inertialess designs have been developed to overcome the stringent mechanical requirements. In these designs the center of focus, or phase center of the antenna is altered using active tuning elements within the antenna horn rather than moving the horn itself.
In U.S. Pat. No. 4,387,378 of Henderson, a series of elements called paracletic elements are disposed about an antenna feed or horn and serve to alter or modulate the position of the phase center for the feed which in turn moves the focus of the antenna. However, this approach requires the control and operation of many active electrical elements through a series of diodes and related control circuitry as well as the isolated mounting of the elements. The result is both electronic and mechanical complexity which increases cost and decreases reliability.
What is needed is a simple method and design for implementing a high speed scanning antenna with minimal complexity and cost while operating very efficiently and reliably.